Simple molecular systems, like water, methane, ammonia, hydrogen, and their mixtures are of para-mount importance for many fields, ranging from energy storage applications to condensed matter and planetary physics [1-2]. These systems are widespread on Earth, in various planetary bodies in the solar system and in newly detected water-rich exoplanets, and constitute an incredibly rich gas resource to be exploited. Due to their relatively simple stoichiometry and electronic structure they also repre-sent key systems for the understanding the physical-chemical behavior of more complex molecular systems. Under the extremely broad range of pressure and temperature conditions experienced in planetary interiors these simple molecular systems and their mixtures display a rich phase diagram, anomalous dynamical, thermal and transport properties, super-ionicity, plasticity and enhanced quan-tum effects [3-12]. In this talk I will review our recent experimental results on the structure and the dynamics of simple molecular systems under extreme conditions probed by neutron, x-ray and light scattering techniques, and will discuss their impact for planetary modelling and energy applications.
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